The life history of red-backed salamanders (Plethodon cinereus) has been intensively studied in the United States, but little information exists for Canadian populations, which limits the ability to perform analyses of latitudinal trends in this species. To investigate variations in body size, age structures, longevity, and growth, we used drift fences to sample populations in four habitats (from mixed to deciduous forests) within a 12 km radius in the Mastigouche Reserve located in Quebec, Canada. During the active season of 1997, we captured, measured and sexed (except neonates) a total of 775 salamanders, and estimated the age of 330 of these specimens using skeletochronology. The population characterized by highest mean body size and/or mean age was from a mixed forest that also harbored the greatest abundance of salamanders. For all populations combined, body size (SVL) ranged from 12–46 mm for males and 12–54 mm for females, and longevity reached 8 yr in females and 9 yr in males. Adult males showed lower mean SVL and mean age than adult females (41.0 mm, 5.2 yr vs. 44.8 mm, 5.8 yr, respectively). Accordingly, von Bertalanffy growth models indicated a higher asymptotic body size and a lower growth coefficient in females. For 7 out of 8 analyses, age was significantly correlated with SVL in animals ≥ 4 yr old; the strength of these correlations was greater in females than in males and significantly correlated with SVL range. Comparisons with other populations reveal that age and size at maturity in P. cinereus increase with latitudes in both sexes. However, females, but not males, show a slight increase in mean adult body size with latitudes, leading to a positive allometric relationship between body size and sexual size dimorphism, the northern populations being more dimorphic. Body increment during the first year of growth was found similar to lowest values reported for other small species of Plethodon from the United States but much reduced compared to conspecific populations from the U.S.A. Factors related to latitude (e.g., temperature, duration of activity season) seem responsible for the observed differences.